The Clinical Genetics Branch (CGB) integrates molecular and clinical observations in cancer genetics into an interdisciplinary approach involving epidemiologic, clinical, genetic, behavioral, statistical and laboratory methods to define the role of susceptibility genes in cancer etiology. The primary goal of this research program is translate recent dramatic advances in molecular genetics into evidence-based management strategies for persons at increased genetic risk of cancer. The central research strategy relies upon the detailed and meticulous assessment of the individual members of cancer-prone families. Hereditary Breast/Ovarian Cancer (HBOC) The first major clinical research project undertaken by CGB represents the next stage in DCEG's long-standing commitment to the study of hereditary breast and ovarian cancer (HBOC). The first priority with regard to these families has been to make clinical predictive genetic testing for BRCA1/2 mutations available to interested family members who had been previous participants in CGB research protocols (Protocol 02-C-0212). All families have been notified of their mutation status, and the process of bringing interested family members to the Clinical Center for genetic risk assessment, counseling, genetic testing and results disclosure is nearing completion. During the past year, ~100 family members have undergone genetic risk assessment, and the majority of those have chosen genetic testing. At the present time, we have 60 hereditary breast/ovarian cancer families under active follow-up. Thirty-five carry deleterious mutations in BRCA1 or BRCA2, and two additional families are segregating the CHEK2 variant known as 1100delC. Thirty-one of the BRCA mutation-carrying families have been under active follow-up for more than 5 years (some as long as 35 years!), and this cohort is currently being analyzed to assess the prospective risks of breast, ovarian, fallopian tube and peritoneal cancers in a set of families that was offered risk-reducing surgery longer before the specific susceptibility genes had been cloned. Our BRCA mutation-negative families comprise a resource for evaluating new candidate highly penetrant breast cancer susceptibility genes. We recently evaluated two such genes (ZBRK1 and BRIP1), and found that neither contributed to the risk of breast and ovarian cancer in these families. DNA from the mutation-positive families is being contributed to an international collaboration which is seeking genetic modifiers of BRCA1 or BRCA2 penetrance. Our study of the prevalence of BRCA1/2 founder mutations in a series of 1000 Ashkenazi Israelis with prostate cancer during 1994 - 1995 documented a two-fold excess of prostate cancer among mutation carriers, providing additional evidence in support of the hypothesis that prostate cancer is part of the spectrum of BRCA-related cancers. No major differences in age at diagnosis or in histopathology between mutation-related and mutation-unrelated have been identified. These data were recently published. We have mounted a new set of psychosocial and behavioral research protocols for these same family members. These projects are addressing issues related to breast cancer screening, early diagnosis, behavioral, educational and psychosocial dynamics related to the process of genetic risk assessment and testing. Under consideration, but not yet implemented, are studies of endogenous hormones as contributors to the risk of hereditary breast cancer, and decision-making by family members related to the use of tamoxifen as a breast cancer chemoprevention strategy. This activity draws upon the expertise of our highly experienced staff, which includes a genetic counselor, a psychiatric social worker and a cancer genetics research nurse.